1. Field of the Invention
The invention relates to voltage clamps.
2. Description of Prior Art
The invention relates in particular to voltage clamps for single-ended flyback convertors that limit the peak of switching voltages generated at turn-off of a switch connected to a normal primary winding of a flyback transformer. Conventionally a so-called "RCD clamp" is used. The RCD clamp includes a resistor, a capacitor and a diode where the automatic forward conduction of the diode, at a predetermined voltage differential, limits the voltage developed immediately after the switch (comprising a MOSFET or bipolar transistor, for example) is turned OFF. Significant power losses can occur, especially at more desirable and lower clamp voltages, when an RCD clamp is used.
So-called "active voltage clamps" are known and include a bidirectional switch and a relatively large capacitor which are arranged so as to allow energy stored in leakage inductance to be recycled. This reduces the power loss in the voltage clamp but the circuit complexity and cost make the active clamp unsuitable for low-cost power supplies.